2018-03-06T19:54:32ZAbsorption of Microwaves by Atmospheric Gaseshttp://hdl.handle.net/1721.1/68611
Absorption of Microwaves by Atmospheric Gases
Rosenkranz, Philip
The theory of absorption of microwave emission by common atmospheric gases is reviewed.
1993-01-01T00:00:00ZOptical Communication Through the Turbulent Atmosphere with Transmitter and Receiver Diversity, Wavefront Control, and Coherent Detectionhttp://hdl.handle.net/1721.1/62578
Optical Communication Through the Turbulent Atmosphere with Transmitter and Receiver Diversity, Wavefront Control, and Coherent Detection
Puryear, Andrew Lee
Free space optical communication through the atmosphere has the potential to provide
secure, low-cost, rapidly deployable, dynamic, data transmission at very high rates.
However, the deleterious e ects of turbulence can severely limit the utility of such a
system, causing outages of up to 100 ms. For this thesis, we investigate an architecture
that uses multiple transmitters and multiple coherent receivers to overcome these
turbulence-induced outages. By controlling the amplitude and phase of the optical
eld at each transmitter, based on turbulence state information fed back from the
receiver, we show that the system performance is greatly increased by exploiting the
instantaneous structure of the turbulence. This architecture provides a robust highcapacity
free-space optical communication link over multiple spectral bands, from
visible to infrared.
We aim to answer questions germane to the design and implementation of the
diversity optical communication architecture in a turbulent environment. We analyze
several di erent optical eld spatial modulation techniques, each of which is based
on a di erent assumption about the quality of turbulence state information at the
transmitter. For example, we explore a diversity optical system with perfect turbulence
state information at the transmitter and receiver that allocates transmit power
into the spatial modes with the smallest propagation losses in order to decrease bit
errors and mitigate turbulence-induced outages. Another example of a diversity optical
system that we examine is a diversity optical system with only a subset of the
turbulence state information: this system could allocate all power to the transmitter
with the smallest attenuation.
We characterize the system performance for the various spatial modulation techniques
in terms of average bit error rate (BER), outage probability, and power gain
due to diversity. We rst characterize the performance of these techniques in the
idealized case, where the instantaneous channel state is perfectly known at both the
receiver and transmitter. The time evolution of the atmosphere, as wind moves tur-
3
bules across the propagation path, can limit the ability to have perfect turbulence
state knowledge at the transmitter and, thus can limit any improvement realized by
optical eld spatial modulation techniques. The improvement is especially limited if
the latency is large or the feedback rate is short compared to the time it takes for
turbules to move across the link. As a result, we make successive generalizations,
until we describe the optimal system design and communication techniques for sparse
aperture systems for the most general realistic case, one with inhomogeneous turbulence
and imperfect (delayed, noisy, and distorted) knowledge of the atmospheric
state.
Thesis Supervisor: Vincent W. S. Chan
Title: Joan and Irwin M. Jacobs Professor of Electrical Engineering and Computer
Science
2011-05-02T00:00:00ZGenerating Pictures from Waves: Aspects of Image Formationhttp://hdl.handle.net/1721.1/54732
Generating Pictures from Waves: Aspects of Image Formation
Accardi, Anthony
The research communities, technologies, and tools for image formation are diverse.
On the one hand, computer vision and graphics researchers analyze incoherent light
using coarse geometric approximations from optics. On the other hand, array signal
processing and acoustics researchers analyze coherent sound waves using stochastic
estimation theory and diffraction formulas from physics. The ability to inexpensively
fabricate analog circuitry and digital logic for millimeter-wave radar and
ultrasound creates opportunities in comparing diverse perspectives on image formation,
and presents challenges in implementing imaging systems that scale in size. We
present algorithms, architectures, and abstractions for image formation that relate
the different communities, technologies, and tools. We address practical technical
challenges in operating millimeter-wave radar and ultrasound systems in the presence
of phase noise and scattering.
We model a broad class of physical phenomena with isotropic point sources. We
show that the optimal source location estimator for coherent waves reduces to processing
an image produced by a conventional camera, provided the sources are wellseparated
relative to the system resolution, and in the limit of small wavelength and
globally incoherent light. We introduce quasi light fields to generalize the incoherent
image formation process to coherent waves, offering resolution tradeoffs that surpass
the traditional Fourier uncertainty principle by leveraging time-frequency distributions.
We show that the number of sensors in a coherent imaging array defines a stable
operating point relative to the phase noise. We introduce a digital phase tightening
algorithm to reduce phase noise. We present a system identification framework for
multiple-input multiple-output (MIMO) ultrasound imaging that generalizes existing
approaches with time-varying filters. Our theoretical results enable the application
of traditional techniques in incoherent imaging to coherent imaging, and vice versa.
Our practical results suggest a methodology for designing millimeter-wave imaging
systems. Our conclusions reinforce architectural principles governing transmitter and
receiver design, the role of analog and digital circuity, and the tradeoff between data
rate and data precision.
Thesis Supervisor: Gregory W. Wornell
Title: Professor of Electrical Engineering and Computer Science
2010-05-07T17:34:28ZAvoiding Interruptions - QoE Trade-offs in Block-coded Streaming Media Applicationshttp://hdl.handle.net/1721.1/50654
Avoiding Interruptions - QoE Trade-offs in Block-coded Streaming Media Applications
ParandehGheibi, Ali; Medard, Muriel; Shakkottai, Srinivas; Ozdaglar, Asu
We take an analytical approach to study Quality of
user Experience (QoE) for video streaming applications. First,
we show that random linear network coding applied to blocks of
video frames can significantly simplify the packet requests at the
network layer and save resources by avoiding duplicate packet
reception. Network coding allows us to model the receiver’s buffer
as a queue with Poisson arrivals and deterministic departures.
We consider the probability of interruption in video playback as
well as the number of initially buffered packets (initial waiting
time) as the QoE metrics. We characterize the optimal trade-off
between these metrics by providing upper and lower bounds on
the minimum initial buffer size, required to achieve certain level
of interruption probability for different regimes of the system
parameters. Our bounds are asymptotically tight as the file size
goes to infinity.
2010-01-12T19:05:11Z